sounded unimaginable to everyone present was she had managed to finish the task in a week

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A. What; how
B. It; how
C. It; that
(答案→)D. What; that
解析：考查主语从句和表语从句：第一空填what引导主语从句，what在主语从句中做主语，第二空填that，连接表语从句，表语从句是完整的，用that连接，不做成分，也不省略。句意：对我们所有的人来说难以想象的是她一个星期能设法完成任务。选D。